Proliferation, migration and invasion of human glioma cells exposed to antifolate drugs.

The present study describes the effects of 2 folate antagonists, methotrexate (MTX) and the lipophilic antifolate trimetrexate (TMX) on 2 permanent human glioma cell lines (GaMg and D-54Mg) grown as monolayers and as multicellular tumor spheroids. In addition, the effects of drug exposure on tumor cell invasion was studied using a three-dimensional organ co-culture system. In monolayer cultures, TMX was a more potent inhibitor of cell growth than MTX, especially towards the GaMg cell line. The 2 drugs, however, showed similar cytotoxicity as assessed by the plating efficiency assay. Reduced ability of directional migration of cells on a plastic surface was seen by either antifolate usually at concentrations to 10-fold higher than those exerting a cytotoxic effect in the plating efficiency assay. TMX was somewhat more potent than MTX as an inhibitor of spheroid growth. When tumor spheroids were exposed to MTX or TMX at concentrations that caused 65 to 70% inhibition of cell migration, there was a latent period of 4 to 5 days before inhibition of spheroid growth ensued. Invasion was investigated in a co-culture system, where tumor spheroids were confronted with fetal rat brain cell aggregates. Neither drug reduced tumor cell invasion, although histological examination revealed toxic effects both in GaMg and in D-54Mg spheroids. We conclude that spheroids from human glioma cells were less sensitive to the antifolates than monolayers. For both drugs a latency period was observed before inhibition of spheroid growth. The spheroids retained their ability to invade normal brain tissue when exposed to levels of folate antagonists inhibiting spheroid growth.